1. Technical Field of the Invention
The present invention relates to a gas turbine power generation facility for maintaining an operation of the power generation facility, and securing a power supply of an important load, when an excessive torque is generated in a generator because of a momentary voltage drop or service interruption of a commercial power supply system.
2. Description of the Related Art
With an accident caused by a thunderstorm, and the like in a commercial power supply system, a phenomenon occurs that a voltage of a power line momentarily and remarkably drops. This voltage drop is referred to as a “momentary voltage drop”. In this case, in order to minimize a damage of a power generation facility and secure a power supply of an important load of a factory, an apparatus for detecting the accident at a high speed and disconnecting the commercial power supply system is disposed in some case. However, even when the apparatus is disposed, but when a parallel off speed is sufficiently fast, the voltage of a power receiving end momentarily and remarkably drops.
A continuation time of the momentary voltage drop is usually about one second or less, and a frequency largely differs with districts. However, even with the momentary voltage drop having a low frequency, an industry (e.g., semiconductor industry) having a factory where a voltage change is not permitted under a demand of a high-voltage power reception is sometimes seriously influenced. Therefore, in the industry, there has been a strong demand for a power generation facility in addition to the commercial power supply, and for the power supply of the important load of the factory steadily secured even during the momentary voltage drop.
FIG. 1 is a schematic diagram of a gas turbine power generation facility which has heretofore been used as a power supply facility. In FIG. 1, reference numeral 1 denotes a motor such as a gas turbine, 2 denotes a pinion gear, 3 denotes a wheel gear, 4 denotes a shaft coupling, and 5 denotes a generator. The motor 1 rotates/drives the pinion gear 2, meshes with the wheel gear 3 to reduce a speed, and rotates/drives the generator 5 via the shaft coupling 4 to generate a power.
FIG. 2 is an enlarged view of a part A of FIG. 1. As shown in the drawing, the conventional wheel gear 3 is constituted by supporting a center shaft 3a with bearings 3b of opposite ends, and the shaft coupling 4 includes intermediate members 6a, 6b, shear pin 7 for connecting the members, deflection element 8, and the like. The center shaft 3a of the wheel gear 3 is connected to a drive shaft 5a of the generator 5 via the deflection element 8 and a slight deviation of a shaft center is permitted. When a torque not less than an allowable torque acts, the shear pin 7 is constituted to cut and an excessive torque is prevented from acting on the motor 1. Furthermore, in this example, the intermediate members 6a, 6b are supported by a bearing 9, rotations of the center shaft 3a and drive shaft 5a are supported after cutting the shear pin 7, and each shaft is prevented from being damaged.
However, in the above-described gas turbine power generation facility, the power generation facility operates in parallel to the system. When the momentary voltage drop is generated in the system, an excessive electric torque is generated in the generator 5. This causes a problem that the shear pin 7 disposed to protect the motor is damaged. That is, the motor has a torsional strength of an axle necessary for transmitting a maximum output thereof, and momentarily allows the transmission of a torque which is several times as large as a rated torque. However, a short circuit accident of the generator, momentary voltage drop and service interruption on a system side, and the like generate the excessive electric torque in the generator. When a transient response torque exceeds the allowable torque of the motor, the shear pin between the motor shaft and the generator shaft breaks, and there is a problem of much recovery time. Moreover, there is a problem that the shear pin disadvantageously breaks by an accumulated metal fatigue even with a relatively small momentary voltage drop (10 to 30%).